1. Field of the Invention
The invention relates to a starter motor assembly for starting an engine and, more particularly, to an engagement and disengagement mechanism for a coaxial starter motor assembly. This application is being filed concurrently with U.S. patent application Ser. No. 10/002,167, entitled Coaxial Starter Motor Assembly Having a Return Spring Spaced From the Pinion Shaft, with inventors David A. Fulton and James D. Stuber, and assigned to Delco Remy America, Inc.
2. Background of the Invention
Starter motor assemblies to assist in starting engines, such as engines in vehicles, are well known. The conventional starter motor assembly broadly includes an electrical motor and a drive mechanism, which generally includes a mechanism for engaging and disengaging a pinion-type gear with an engine flywheel. The electrical motor is energized by a battery upon the closing of an ignition switch. The drive mechanism transmits the torque of the electrical motor through various components to the engine flywheel, thereby cranking the engine until the engine starts.
In greater detail, the closing of the ignition switch (typically by turning a key) energizes a solenoid with low current. Energization of the solenoid moves a metal solenoid shaft or plunger in an axial direction. The movement of the solenoid plunger closes electrical contacts, thereby applying full power to the electrical motor. The movement of the solenoid plunger also biases the pinion-type gear into engagement with a ring gear of the engine flywheel. Once the vehicle engine is started, the operator of the vehicle will open the ignition switch. The solenoid is thus turned off (i.e., deenergized), but the electrical contacts are still closed. To prevent run-on of the electrical motor, and subsequent damage, the engagement and disengagement mechanism must be designed to break the electrical contacts and disengage the pinion-type gear from the engine flywheel.
Starter motors assemblies can be either xe2x80x9cbiaxialxe2x80x9d or xe2x80x9ccoaxial.xe2x80x9d These terms relate to the location of the solenoid and the solenoid plunger with respect to the armature shaft of the electrical motor. In a biaxial starter motor, the solenoid and the solenoid plunger are attached to the motor casing, with the solenoid plunger spaced away from and generally parallel to the armature shaft. In a coaxial starter motor, the solenoid is typically placed in the motor casing so that the solenoid plunger is aligned in the same axis with the armature shaft. The coaxial assembly is considered to be more compact and universally adaptable than the biaxial assembly. The present invention is directed to a coaxial assembly.
Once the electrical contacts are closed and full power is applied from the battery to the electrical motor, the motor""s armature shaft subsequently rotates at a high speed. A planetary gear assembly, coupled to the armature shaft, reduces the speed of rotation of the armature shaft. The planetary gear assembly includes a drive shaft that rotates at that reduced speed. The end of the drive shaft opposite the planetary gear assembly is coupled with a pinion, preferably by a pinion shaft. Thus, the pinion rotates due to the rotation of the planetary gear drive shaft, which in turn rotates (again, at a reduced speed) due to the rotation of the electrical motor armature shaft.
Starter motor assemblies typically include a one-way clutch that is utilized to allow the planetary gear drive shaft to rotate at higher speeds and/or in the opposite direction from the cranking of the engine and to ensure that these higher rotational speeds or opposite directional velocities are not transmitted to the electrical motor armature shaft. In coaxial starter motor assemblies, the clutch is sometimes built around a ring gear positioned between the planetary gear drive shaft and the electrical motor armature shaft.
As stated above, energization of the solenoid also moves the solenoid plunger in the axial direction to move the pinion into engagement with the engine flywheel. In coaxial starter motor assemblies, typically the plunger is coupled to the pinion such that the movement of the plunger in turn moves the pinion in that same axial direction.
The pinion includes a plurality of gear teeth on its external surface for engagement with the engine flywheel. Thus, when the pinion is biased toward engagement of the flywheel and is rotating, the engagement of the pinion with the ring gear of the flywheel in turn causes the flywheel to rotate, thereby cranking the vehicle engine.
For the energization of the solenoid assembly to move the solenoid plunger and hold the plunger for pinion-flywheel engagement, solenoid assemblies typically utilize two coils, a pull-in coil and a hold-in coil. In particular, both coils energize the plunger of the solenoid assembly to bias the plunger in the axial direction for engagement with the engine flywheel. The hold-in coil then holds the plunger in place to hold the pinion in the engagement position with the ring gear of the engine flywheel.
After the operator of the vehicle opens the ignition switch, which deenergizes the solenoid assembly, the magnetic field that caused the solenoid plunger to move decreases and at some point is overcome by a return spring. In particular, the return spring continually pushes against the pinion away from engagement with the engine flywheel. However, it is only at those times when the force of the return spring is greater than the magnetic field generated by the solenoid biasing the plunger toward the flywheel, and an axial thrust force when the engine fails to start (discussed below), that the pinion is moved away from engagement from the flywheel.
The axial thrust force is generated by the torque of the electrical motor. In most coaxial starter motor assemblies, the pinion shaft is a bore with helical internal splines that correspond with helical external splines on the planetary gear drive shaft for engagement of the pinion shaft and the planetary gear drive shaft. The direction of the helical splines are typically opposite the direction of rotation of the pinion and the pinion shaft in order to facilitate the engagement and disengagement of the pinion and the ring gear of the engine flywheel. When torque is transmitted through the helical splines, an equal and opposite axial thrust force is generated on the splines. Neglecting friction between the splines of the pinion shaft and the planetary gear drive shaft, the axial thrust force may be determined by the following equation:
Fa=2xcfx80(T/L), where: 
Fa=the axial thrust force (Newtons)
T=applied torque (Newton-millimeters), and
L=lead of helical spline (millimeter/revolution).
The axial thrust force pulls the pinion into engagement with the ring gear when a cranking torque is applied and tends to push the pinion out of mesh from the ring gear when the engine starts due to overrunning torque. A typical cranking torque is about 15,000 N-m and a typical spline lead is about 130 mm. Using these values, a typical axial thrust force is about 725 N that is pulling the pinion into the ring gear.
If the engine fails to start, to prevent run-on of the electrical motor, which will be drawing a heavy electrical current, typically over 300 amps, the electrical contacts should be allowed to open when the ignition switch is opened. In many coaxial starter motor assemblies, the solenoid plunger is rigidly attached to the pinion shaft. However, if the plunger can not move independently of the pinion shaft, then the return spring would have to exert a force of greater than 725 N in the direction away from engagement of the pinion and the ring gear to overcome the axial thrust force that is pulling the pinion into engagement with the ring gear. To achieve such a high spring force, the spring would have to be large, which would result in the need for a larger solenoid. Both a larger spring and a larger solenoid would result in a more expensive starter motor assembly.
In order to open the electrical contacts to prevent run-on of the electrical motor in the situation where the engine fails to start, the solenoid plunger should be capable of moving independently of the pinion shaft in order to break the electrical contacts before the pinion gear is disengaged from the engine flywheel.
The present invention is directed to a coaxial starter motor assembly that includes a housing. An electrical motor is provided in the housing that has a rotatable armature shaft. A rotatable drive shaft is provided that is engageably linked with the armature shaft. A pinion assembly is provided in the housing that is engageable at one end with the drive shaft and includes a pinion at the other end engageable with a flywheel of an engine. A solenoid assembly is provided in the housing for selectively energizing the electrical motor. The solenoid assembly is coaxial with the drive shaft. The solenoid assembly includes a plunger having a bore. The plunger is engageable with the pinion assembly to move the pinion assembly including the pinion into engagement with the flywheel. The plunger is also engageable with a moveable contact to move the moveable contact to electrically connect with a pair of fixed contacts. A return spring is provided that is positioned at least in part within the bore of the plunger of the solenoid assembly for moving the pinion assembly including the pinion away from engagement with the flywheel. The return spring is spaced from the pinion assembly. Energization of the solenoid assembly moves the plunger to move the pinion assembly to engage the pinion with the flywheel. Upon deenergization of the solenoid assembly, the return spring moves the pinion assembly to move the pinion from engagement with the flywheel. In addition, upon deenergization of the solenoid assembly, the plunger is capable of moving independently of the pinion assembly to thereby break the electrical connection between the moveable contact and the fixed contacts before the return spring moves the pinion assembly to move the pinion away from engagement with the flywheel.
The plunger is capable of moving independently of the pinion assembly to thereby break the electrical connection between the moveable contact and the fixed contacts while the pinion is in engagement with the flywheel. This prevents run-on of the electrical motor if the engine fails to start upon engagement of the pinion and the flywheel.
The present invention is also directed to a coaxial starter motor assembly that includes a housing. An electrical motor is provided in the housing that has a rotatable armature shaft. A rotatable drive shaft is provided that is engageably linked to the armature shaft. A pinion assembly is provided in the housing. The pinion assembly includes a pinion shaft that is engageable at one end with the drive shaft and includes a pinion at the other end engageable with a flywheel of an engine. The pinion shaft includes a groove formed around an external surface of the pinion shaft. A solenoid assembly is provided in the housing for selectively energizing the electrical motor. The solenoid assembly is coaxial with the drive shaft. The solenoid assembly includes a plunger having a bore. The plunger is engageable with the pinion shaft to move the pinion into engagement with the flywheel. The plunger is also engageable with a moveable contact to move the moveable contact to electrically connect with a pair of fixed contacts. A return spring is provided that is positioned around the pinion shaft without contacting the pinion shaft. The return spring is positioned at least in part within the bore of the plunger of the solenoid assembly. A contact member is provided that is positioned within the groove formed around the external surface of the pinion shaft. The contact member also is positioned within the bore of the plunger of the solenoid assembly. Energization of the solenoid assembly moves the plunger which in turn moves the contact member which in turn moves the pinion shaft to thereby engage the pinion with the flywheel. Upon deenergization of the solenoid assembly, the return spring moves the contact member which in turn moves the pinion shaft to move the pinion from engagement with the flywheel. Upon deenergization of the solenoid assembly, the plunger is capable of moving independently of the pinion shaft to thereby break the electrical connection between the moveable contact and the fixed contacts before the return spring moves the contact member to move the pinion shaft to move the pinion away from engagement with the flywheel.
In one embodiment, the coaxial starter motor assembly includes a plunger stop assembly provided around the pinion assembly. The plunger seats against the plunger stop assembly when the plunger has moved from a rest position to its farthest axial position toward engagement of the pinion and the flywheel.
In one embodiment, D, a maximum distance that the pinion shaft may travel from a rest position when moving in an axial direction toward engagement of the pinion and the flywheel, is determined; G, a distance that the plunger may still move in the axial direction toward engagement of the pinion and the flywheel after the moveable contact electrically connects with the pair of fixed contacts, is determined; H, a minimum distance between an internal spline stop of the pinion shaft and an external spline axial stop on the drive shaft, is determined, wherein the distance H is equal to a distance that the pinion shaft may still travel after the plunger seats against the plunger stop assembly; and K, a minimum distance to open the moveable contact from the fixed contacts to thereby break the electrical connection between the moveable contact and the fixed contacts when the pinion shaft is positioned in its farthest axial position toward engagement of the pinion and the flywheel, is determined. Then, the following three equations are solved to determine distances A, B, and C, wherein A is a maximum distance that the plunger may move independent of the pinion shaft relative to the pinion shaft, B is a maximum distance between the moveable contact and the fixed contacts, and C is the maximum distance that the plunger may travel from a rest position when moving in the axial direction toward engagement of the pinion and the flywheel:
(1) B=K+D,
(2) C=G+B, and
(3) A=Hxe2x88x92D+C.
The distance G is also the minimum distance that a contact overtravel spring may be compressed.
The present invention is also directed to a method of operating a coaxial starter motor assembly. The coaxial starter motor assembly includes a housing; an electrical motor provided in the housing having a rotatable armature shaft; a rotatable drive shaft engageably linked with the armature shaft; a pinion assembly provided in the housing engageable at one end with the drive shaft and includes a pinion at the other end engageable with a flywheel of an engine; a solenoid assembly provided in the housing for selectively energizing the electrical motor, wherein the solenoid assembly is coaxial with the drive shaft, the solenoid assembly includes a plunger having a bore, the plunger is engageable with the pinion assembly to move the pinion assembly includes the pinion into engagement with the flywheel, and the plunger is engageable with a moveable contact to move the moveable contact to electrically connect with a pair of fixed contacts; a return spring positioned at least in part within the bore of the plunger of the solenoid assembly for moving the pinion assembly includes the pinion away from engagement with the flywheel, wherein the return spring is spaced from the pinion assembly; wherein energization of the solenoid assembly moves the plunger to move the pinion assembly to engage the pinion with the flywheel; and wherein upon deenergization of the solenoid assembly, the return spring moves the pinion assembly to move the pinion from engagement with the flywheel. The method comprises the step of moving the plunger independently of the pinion assembly upon deenergization of the solenoid assembly to thereby break the electrical connection between the moveable contact and the fixed contacts before the return spring moves the pinion assembly to move the pinion away from engagement with the flywheel if the engine fails to start upon engagement of the pinion and the flywheel.
The present invention is also directed to a method of operating a coaxial starter motor assembly. The coaxial starter motor assembly includes a housing; an electrical motor provided in the housing having a rotatable armature shaft; a rotatable drive shaft engageably linked to the armature shaft; a pinion assembly provided in the housing, the pinion assembly includes a pinion shaft, the pinion shaft engageable at one end with the drive shaft and includes a pinion at the other end engageable with a flywheel of an engine, and the pinion shaft includes a groove formed around an external surface of the pinion shaft; a solenoid assembly provided in the housing for selectively energizing the electrical motor, wherein the solenoid assembly is coaxial with the drive shaft, the solenoid assembly includes a plunger having a bore, the plunger is engageable with the pinion shaft to move the pinion into engagement with the flywheel and the plunger is engageable with a moveable contact to move the moveable contact to electrically connect with a pair of fixed contacts; a return spring positioned around the pinion shaft without contacting the pinion shaft, the return spring is positioned at least in part within the bore of the plunger of the solenoid assembly; and a contact member positioned within the groove formed around the external surface of the pinion shaft, the contact member also is positioned within the bore of the plunger of the solenoid assembly; wherein energization of the solenoid assembly moves the plunger which in turn moves the contact member which in turn moves the pinion shaft to thereby engage the pinion with the flywheel; and wherein upon deenergization of the solenoid assembly, the return spring moves the contact member which in turn moves the pinion shaft to move the pinion from engagement with the flywheel. The method comprises the step of moving the plunger independently of the pinion shaft upon deenergization of the solenoid assembly to thereby break the electrical connection between the moveable contact and the fixed contacts before the return spring moves the contact member to move the pinion shaft to move the pinion away from engagement with the flywheel if the engine fails to start upon engagement of the pinion and the flywheel.
The present invention is also directed to a method of designing a coaxial starter motor assembly. The coaxial starter motor assembly includes a housing; an electrical motor provided in the housing having a rotatable armature shaft; a rotatable drive shaft engageably linked to the armature shaft; a pinion assembly provided in the housing, the pinion assembly includes a pinion shaft, the pinion shaft engageable at one end with the drive shaft and includes a pinion at the other end engageable with a flywheel of an engine, and the pinion shaft includes a groove formed around an external surface of the pinion shaft; a solenoid assembly provided in the housing for selectively energizing the electrical motor, wherein the solenoid assembly is coaxial with the drive shaft, the solenoid assembly includes a plunger having a bore, the plunger is engageable with the pinion shaft to move the pinion into engagement with the flywheel and the plunger is engageable with a moveable contact to move the moveable contact to electrically connect with a pair of fixed contacts; a return spring positioned around the pinion shaft without contacting the pinion shaft, the return spring is positioned at least in part within the bore of the plunger of the solenoid assembly; a contact member positioned within the groove formed around the external surface of the pinion shaft, the contact member also is positioned within the bore of the plunger of the solenoid assembly; and a plunger stop assembly provided around the pinion assembly, wherein the plunger seats against the plunger stop assembly when the plunger has moved from a rest position to its farthest axial position toward engagement of the pinion and the flywheel; wherein energization of the solenoid assembly moves the plunger which in turn moves the contact member which in turn moves the pinion shaft to thereby engage the pinion with the flywheel; wherein upon deenergization of the solenoid assembly, the return spring moves the contact member which in turn moves the pinion shaft to move the pinion from engagement with the flywheel; and wherein upon deenergization of the solenoid assembly, the plunger is capable of moving independently of the pinion shaft to thereby break the electrical connection between the moveable contact and the fixed contacts before the return spring moves the contact member to move the pinion shaft to move the pinion away from engagement with the flywheel.
The method of designing a starter motor assembly includes the step of determining D, a maximum distance that the pinion shaft may travel from a rest position when moving in an axial direction toward engagement of the pinion and the flywheel. The method further includes the step of determining G, a distance that the plunger may still move in the axial direction toward engagement of the pinion and the flywheel after the moveable contact electrically connects with the pair of fixed contacts. The method further includes the step of determining H, a minimum distance between an internal spline stop of the pinion shaft and an external spline axial stop on the drive shaft, wherein the distance H is equal to a distance that the pinion shaft may still travel after the plunger seats against the plunger stop assembly. The method further includes the step of determining K, a minimum distance to open the moveable contact from the fixed contacts to thereby break the electrical connection between the moveable contact and the fixed contacts when the pinion shaft is positioned in its farthest axial position toward engagement of the pinion and the flywheel. Then, the method includes the step of solving the following three equations to determine distances A, B, and C, wherein A is a maximum distance that the plunger may move independent of the pinion shaft relative to the pinion shaft, B is a maximum distance between the moveable contact and the fixed contacts, and C is the maximum distance that the plunger may travel from a rest position when moving in the axial direction toward engagement of the pinion and the flywheel:
(1) B=K+D,
(2) C=G+B, and
(3) A=Hxe2x88x92D+C.
The advantages of the invention will be set forth in the description below, and in part will be apparent from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by the combinations set forth in the attached claims.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.